Function pipe_control_passthrough 

async fn pipe_control_passthrough(
    recv: RecvStream,
    send: SendStream,
    side: ProxySide,
    ctx: &ForwardCtx,
) -> Result<(), ProxyError>

Forward-first control stream pipe.

Bytes are forwarded to the peer the instant they arrive; the parser runs on a cloned copy purely to drive observer events. No hook can rewrite frames on this path because the bytes are already in flight.